Turning roll systems of the type mentioned above generally comprise a pair of drive rollers spaced laterally from each other to frictionally engage opposite sides of a cylindrical workpiece at a first axial location, and a pair of idler rollers spaced laterally from each other to engage opposite sides of the workpiece at a second axial location spaced apart from the first axial location along an axis of rotation of the workpiece. The drive rollers are connected to a motor drive operable to rotate the drive rollers to thereby rotate the workpiece about its axis of rotation, referred to herein as the “workpiece axis.” The idler rollers cooperate with the drive rollers to provide rolling support for the workpiece, but the idler rollers are not motor-driven. Typically, the drive rollers and idler rollers rotate about respective axes of rotation that are parallel to the workpiece axis. Due mainly to imperfections in the cylindrical shape of the workpiece, rotation of the workpiece about the workpiece axis may be accompanied by slight axial drift of the workpiece which can cause misalignment of weld seams.
Conventional anti-drift turning roll systems control the axial movement of the cylindrical workpiece or vessel by shifting the idler rollers vertically or horizontally in proportion to the amount of drift. This method is effective in controlling drift, but may result in significant vertical or horizontal movement of the workpiece which can interfere with the welding process.
Other anti-drift turning roll systems are based on adjusting the axis of rotation of one or more of the rollers to extend obliquely relative to the workpiece axis to introduce an axial force component counteracting the drift. Anti-drift turning roll systems of this type are summarized below.
U.S. Pat. No. 2,865,690 discloses a mechanically self-adjusting system wherein a pair of follower rollers 16 are arranged in abutment one with each end face of a tire 6 fitted around the circumference of the workpiece. The abutment follower rollers 16 are coupled by respective lever arms 15 to a trunnion bracket 9a supporting a roller 8 on one side of the workpiece. The trunnion bracket 9a is connected by a pair of parallel pivotal links 9b to an opposite side trunnion bracket 9a carrying a second roller 8 such that the two trunnion brackets 9a and two links 9b form a parallelogram linkage. When the workpiece is in a desired neutral axial position, the parallelogram linkage is in the form of a rectangle and the axes of rotation a-a of rollers 8 are parallel to the axis of rotation of the workpiece. When axial drift of the workpiece occurs as detected by follower rollers 16, the lever arms 15 transfer motion to the parallelogram linkage such that the rollers 8 and their rotational axes become angled obliquely with respect to the workpiece axis of rotation. A screw-thread effect returns the workpiece to its neutral axial position, and corresponding action of the follower rollers 16 and lever arms 15 returns the parallelogram linkage to its rectangular state.
British Patent No. 940,261 describes various embodiments. In an embodiment illustrated by FIG. 1, one of the four rollers 2 of the turning roll system can be turned by pivoting its sub-frame 4 about a vertical axis to adjust the axis of rotation of the roller 2 out of its neutral orientation parallel to the workpiece axis to an angled orientation nonparallel to the workpiece axis to counter axial drift. Another embodiment illustrated by FIGS. 2 and 3 works in a similar manner, wherein the axle 5 of a compensating roller 6 is mounted to pivot about a vertical axis. FIGS. 4 and 5 show a further embodiment wherein the axle 12 of a compensating roller 13 is mounted for pivotal motion about an axis defined by pivot pin 14 extending normal to the tangential plane at the point of contact between roller 13 and the workpiece. In this embodiment, the roller axis is parallel to the workpiece axis in a neutral configuration, and the roller axis may be pivoted in the tangential plane to be nonparallel to the workpiece axis for countering axial drift. FIG. 6 teaches another embodiment wherein a pair of rollers 25 on opposite sides of the workpiece are mounted on a common sub-frame 28 mounted for pivotal motion about a vertical pivot axis defined by pivot pin 29. The rotational axes of rollers 25 are parallel to the workpiece axis when the rollers 25 are in a neutral state, and the rotational axes of rollers 25 are adjusted to be nonparallel to the workpiece axis by pivoting the sub-frame 28 about pivot pin 29. Finally, an embodiment depicted in FIG. 7 teaches the use of abutment rollers 52 engaging end faces of the workpiece and coupled by a linkage 53 to pivot a sub-frame of compensating roller 50 about a vertical axis. Here again, the roller axis is parallel to the workpiece axis in a neutral state, and is urged out of parallel to counter axial drift of the workpiece.
British Patent No. 1,034,201 discloses an anti-drift adjustment mechanism wherein a trunnion bracket 12 carrying a pair of rollers 13 for engaging a side of the workpiece is pivotally mounted in a base or frame 10. The trunnion bracket 12 is coupled to a screw mechanism 20, 21, 22 such that rotation of the screw pivots the trunnion bracket 12 to adjust the roller axes slightly out of a neutral orientation parallel to the workpiece axis to an oblique orientation in which the rollers counteract axial drift of the workpiece.
British Patent No. 2,106,810 describes a turning roll system wherein a set of rollers 20 for engaging the workpiece is carried on a support 30 mounted to pivot about a generally vertical shaft 32 that is tilted laterally inward toward the workpiece. Rollers 20 rotate about axes that are parallel to the workpiece axis when the support 30 is in a neutral pivot position. A stylus 22 is biased to engage an end face of the workpiece to sense axial drift, and a signal indicative of axial drift is transmitted to electronic control means for operating a motor 44 and gearing to pivot support 30 about shaft 32 such that the roller axes are adjusted out of parallel with the workpiece axis to oppose the sensed axial drift.
U.S. Pat. No. 4,407,621 presents a turning roll system wherein three sets of rollers 24 are mounted on axially displaceable carriages 3, and a fourth set of rollers 24 is mounted on an axially fixable carriage. A mechanism 25, 27, 29 for each carriage 3 converts an axial movement of the carriage to a swivel movement of a roller holder 15, 20 on the carriage about a swivel axis 16 to adjust the roller axes out of a neutral orientation parallel to the workpiece axis to a drift counteracting orientation nonparallel to the workpiece axis.
While the solutions discussed above provide generally adequate results, they are mechanically complex. For example, the roller supports must be mounted to pivot about an axis that is vertical or generally vertical (inclined toward the workpiece), and a pivoting mechanism for the entire roller support must be provided.
In each case, the prior art solution provides a neutral orientation of the roller axes that is parallel to the workpiece axis.
It is also noted that none of the prior art systems discussed above pivots the roller support on one side of the workpiece in an opposite pivot direction from the roller support on the other side of the workpiece to impart additive axial force components to evenly oppose axial drift.